The present invention relates, in general, to an internal combustion engine, and more particularly to a hydraulic device of an internal combustion engine to adjust the rotation angle of a camshaft in relation to a crankshaft.
Nothing in the following discussion of the state of the art is to be construed as an admission of prior art.
German patent publication no. DE 101 34 320 A1 describes a hydraulic device for adjusting the rotation angle of a camshaft in relation to a crankshaft of an internal combustion engine. The device includes a rotor, which is configured in the form of a vane wheel secured to the camshaft by a central fastening screw, and a stator which is closed in fluid-tight manner by an end wall, which forms part of a housing in surrounding relationship to the stator, and by a timing pulley, which is driven by the crankshaft. The stator surrounds the rotor and rotates in synchronism with the timing pulley. Substantially radially extending sidewalls in the stator permit only a limited rotation angle of the rotor and form with the stator several pressure chambers which can be supplied with pressure medium or purged from pressure medium.
The components of this hydraulic device are made predominantly of steel or iron through sintering or material removing machining processes. As a result, the hydraulic device is very massive. In addition, manufacturing costs for making the sintered components by the material removal process are extensive, and undesired external oil leaks can be experienced as a consequence of the porosity of the sintered components.
Another reason for making the components of hydraulic devices heavy and massive is the belief that thin wall thicknesses in sintering metallurgy would cause problems as far as density distribution, strength and stiffness are concerned, especially when the wall thickness fluctuates, and that complex shapes with different fill heights can normally be realized only by using expensive slides in the tool. Hydraulic devices made by a material removing process encounter similar problems. In other words, complex shapes to suit the load at hand can be made only by a complicated machining process.
One approach to reduce the mass of the hydraulic device involves the manufacture of components of the hydraulic device from aluminum or aluminum alloy or a different lightweight metal. Examples for this approach include German patent publication nos. DE 101 48 687 A1 or DE 101 34 320. This approach has, however, the drawback that the leakage gap increases in view of the presence of different thermal expansion coefficients when the components heat up, resulting in excessive leaking. Moreover, aluminum is subjected to greater deformation than steel or iron under load when same dimensions are involved. In particular, the use of screw fasteners to bolt the individual parts together requires the provision of large enough gaps to accommodate the deformation. The need for screw fasteners, however, not only also complicates the assembly and incurs added costs but also adversely affects the force flux.
It would therefore be desirable and advantageous to provide an improved device of an internal combustion engine for adjusting the rotation angle of a camshaft in relation to a crankshaft, to obviate prior art shortcomings and to accomplish an overall mass reduction while effectively minimizing leakage.